Our studies in the last 2 years have shown that HSV-2 reactivation has both a more rapid and frequent pace of onset and clearance than previously appreciated; more than 40% of all HSV-2 reactivations last <6 hours; these short episodes of reactivation are characterized by the rapid release of 103 to 104 copies of HSV-2 DMA onto mucosal surfaces and accompanied by the rapid clearance of virus by the host. A similar pattern of reactivation appears to occur for oral-labial HSV infection. Host clearance of mucosal HSV varies considerably between individual from <0.3 logs of HSV DMA/hour to 2 logs/hour. Recent studies mapping CDS T cell responses in situ indicate that HSV-2 specific T cells in the periphery persist at the dermalepidermal junction contiguous to neuronal endings and that the host immune responses can contain viral replication even before it causes mucosal ulcerations. This project is directed at characterizing the frequency of rapidly cleared mucosal HSV infections by anatomic site, gender, viral subtype (HSV-1 versus HSV-2), and degree of immunosuppression (immunocompetent patients, pregnant women, HIV positive patients on/off HAART, and patients post hematopoietic stem cell transplantation (HSCT). These studies will define the frequency in which rapidly cleared episodes occur in these patient populations. We will then enroll persons with rapid and slow clearance rates into mechanistic studies to define the association between clearance rate and the anatomic site and functional characteristics of HSV-2 specific CD8+ T-cells in skin. We will test the hypothesis that clearance rates of mucosal HSV reactivation will be inversely correlated with the presence of HSV-2 specific CD8+T cells in genital skin at the site of reactivation. Studies to define the functional characteristics of HSV- 2 specific cells that appear to participate in immune surveillance will also be performed. In addition, pilot studies to define if increasing doses of anti-HSV therapy will eliminate these short bursts of mucosal HSV reactivation and provide more optimal suppression of HSV-2 are proposed. Among HSV-2/HIV-1 co infected persons, we will define the temporal dynamics between HSV-2 reactivation and HIV-1 replication on mucosal surfaces using a newly developed, highly sensitive HIV-1 RNA assay and evaluate in sequential biopsy samples the role HSV-2 specific CD8+ T-cells play in resolution of HSV-2 in the HIV infected patient. We will test the hypothesis that dosing regimens that minimize sub clinical HSV-2 reactivation will produce more sustained reduction in HIV RNA among HIV co-infected persons with CD4 T-cell counts >400 cells/ml. Project 1 is designed to define and develop new strategies for controlling HSV-2 infection and identify high risk groups for which improved medical and public health management strategies can be initiated.